Figure 1:
Adiabatic pumping in (left) the waveguide device studied by Kraus et al. and (right) in the classical geometry Laughlin used to describe the integer quantum Hall effect. In the waveguide, light (red) entering at one end of the device is pumped to the other end. In Laughlin’s picture, a magnetic field (H0) pumps charges in a current along the ribbon from one edge of the ribbon to the other, generating a voltage perpendicular to the current.